The present invention generally relates to a system for controlling data transmission in an ATM (asynchronous transfer mode) switching network.
There is known an ATM switching network in which data is transferred in an asynchronous transfer mode. In the ATM switching network, data is divided into predetermined-length data pieces. A header is added to each predetermined-length data piece so that a cell is formed. In the ATM system, cells are transferred. ATM switching networks realize connection oriented services. Thus, ATM switching networks have advantages presented by the line switching and packet switching. However, ATM switching networks are not oriented to connectionless services as provided by packet switching.
In order to realize connectionless services by using an ATM switching network, it is necessary to define a fixed virtual channel in the ATM switching system since the ATM switching network is a connection-oriented services network, as described above.
Referring to FIG.1, an ATM switching network 63 is provided with a handler 62. A plurality of terminal equipment devices (hereinafter simply referred to as terminals) 61-1 - 61-n are coupled to the ATM switching network 63. It will be noted that for the sake of simplicity, terminal adapters, which derive predetermined-length cells from data and execute the reverse process, are omitted from the illustration. The handler 62 sets addresses of the terminals 61-1 - 61-n on the ATM switching network 63 and corresponding fixed virtual channels (illustrated by the broken lines) by using a network management function. It will be noted that virtual channels are called virtual circuits for packet data. Further, the handler 62 assigns virtual channel identification numbers to the terminals 61-1 - 61-n.
Each of the terminals 61-1 - 61-n divides data into cells, each including the called party address, by using the virtual channel identification number assigned to the sending terminal, and sends the cells to the handler 62 through the ATM switching network 63. The handler 62 assembles received cells and identifies the called party address from the assembled original data. Then, the handler 62 seeks a corresponding virtual channel based on the identified party address. After that, the handler 62 divides the assembled data into cells again by using the virtual channel identification number of the related virtual channel, and sends the cells to the destination terminal. With the above-mentioned arrangement, it is possible to transfer data between the terminals through the ATM switching network 63 by the connection-oriented services as provided by the packet switching system.
Referring to FIG.2, a plurality of terminals 64-1 - 64-n are connected to an ATM switching network 65. It will be noted that no handler is coupled to the ATM switching network. Fixed virtual channels illustrated by broken lines are provided between each pair of terminals which may communicate with each other. It can be considered that the system shown in FIG.2 distribute the function of the handler 62 shown in FIG.1 to the terminals 64-1-64-n. The terminals can communicate with each other through the fixed virtual channels via which cells are transferred.
However, the conventional system shown in FIG.1 has the disadvantages described below. It is necessary to provide the number of virtual channels equal to the number of terminals accommodated in the ATM switching network 63. When terminals are added to the system, the same number of virtual channels must be provided in the ATM switching network 63. There is a limit of the number of virtual channels provided in the ATM switching network 63. For this reason, the number of terminals which can be coupled to the ATM switching network 63 is also limited. It should be noted that virtual channels are provided even for some terminals which are not often used. When terminals are added to or removed from the ATM switching network 63, the handler 62 must be modified so that the procedure for setting or releasing virtual channels are changed. Further, the handler 62 is required to have a large data processing ability to assemble and disassemble cells. Thus, the system employing the handler 62 is expensive.
The conventional system shown in FIG.2 has the disadvantages described below. As described previously, virtual channels are provided between terminals which may communicate with each other. When a large number of terminals may communicate, it is necessary to provide a large number of virtual channels in the ATM switching network 65. It will be noted that a limited number of virtual channels is provided in the ATM switching network 65. Thus, the number of terminals which can be accommodated in the ATM switching network 65 is also limited. When terminals are added to or removed from the ATM switching network 65, all virtual channels related to these terminals must be provided or removed.